Businesses and individuals increasingly rely on Voice over Internet Protocol (VoIP) for communications. In such systems, Session Initiation Protocol (SIP) may be used as an application-layer control (e.g., signaling) protocol for creating, modifying, and terminating sessions (e.g., phone calls) with one or more participants. In addition to phone calls, SIP and IP may be used for video calls, multimedia conferences, and instant messaging conferences.